The group, founded by jailed human rights lawyer Mohannad al-Hassani, said the U.N. Security Council must convene to start proceedings against Syrian officials in the International Criminal Court and "reign in the security apparatus."

"This savage behavior, which is aimed at keeping the ruling clique in power at the expense of a rising number of civilian lives, calls for immediate international action beyond condemnations," Sawasiah said in a statement sent to Reuters.

"The murderers in the Syrian regime must be held accountable. The rivers of blood spilled by this oppressive regime for the past four decades are enough," the statement said.

Sawasiah's board includes Syrian philosophy professor Sadeq Jalal al-Azem, whose book "Self-criticism after the defeat" helped set the stage for a revival in Arab political thought after Israel's victory in the 1967 Middle East War.